Technical Field
The present invention generally relates to hydrocracking of hydrocarbon streams to produce lower boiling compounds. More particularly, the present invention relates to a high shear system and process for improving hydrocracking of a feedstock to produce simpler hydrocarbons.
Background of the Invention
In petroleum refining and chemistry, cracking is the process whereby complex organic molecules such as heavy hydrocarbons are broken down into simpler light hydrocarbons. The conversion occurs via the breaking of carbon-carbon bonds in the precursor molecules. The rate of cracking and the end products formed depend greatly on the temperature as well as on the presence of any catalysts. Oil refinery cracking processes allow the production of “light” products such as LPG and gasoline from heavier crude oil distillation fractions such as gas oils and residues.
Cracking may be performed by catalytic cracking or thermal cracking. In thermal cracking, elevated temperatures (˜800° C.) and pressures (˜700 kPa) are used. Hydrogen-rich products are formed at the expense of heavier molecules which condense and become depleted of hydrogen. Catalytic cracking involves the use of acid catalysts, typically solid acid catalysts, such as silica-alumina and zeolites. Hydrocracking is a major process for the production of jet fuel, gasoline components and LPG.
Hydrocracking is a catalytic cracking process assisted by the presence of an elevated partial pressure of hydrogen. Petroleum refinery hydrocracking processes are well known and developed. Such processes upgrade mixtures of hydrocarbons to supply more valuable product streams. The products of this process are saturated hydrocarbons. Depending on reaction conditions (temperature, pressure, and catalyst activity) the cracking products range from ethane, LPG to heavier hydrocarbons comprising mostly isoparaffins. Hydrocracking is normally facilitated by a dual function catalyst that is capable of rearranging and breaking hydrocarbon chains as well as adding hydrogen to aromatics and olefins to produce naphthenes and alkanes.
Severity of hydrocracking is increased by operating with increasingly acidic catalysts and possibly at higher temperatures and longer contact times than in hydrotreating. Increased hydrogen pressure controls deposits and catalyst fouling. Unlike thermal or catalytic cracking, hydrocracking decreases the molecular weight of aromatic compounds and fills a specific need for processing streams high in aromatic material, such as cycle stocks from catalytic or thermal cracking, coker products, or coal liquids. For example, catalytic cycle stock can be cracked to a naphtha fraction that is an excellent feed for catalytic reforming to make premium-octane gasoline or petrochemical aromatic material. Major products from hydrocracking are jet fuel, diesel, relatively high octane rating gasoline fractions and LPG. These products may have a very low content of sulfur and contaminants.
Fuel oil is a fraction obtained via petroleum distillation, either as a distillate or residue. Distillate fuel oils are distilled from crude oil. Gas oil refers to the process of distillation. The oil is heated, becomes a gas and condenses as gas oil. Gas oil is thus differentiated from residual oil. The terms heavy fuel oil and residual fuel oil are what remains of the crude oil after gasoline and the distillate fuel oils are extracted through distillation. Hydrocracking is used extensively on distillate stocks. The hydrocracking process is applied to refinery stocks for premium-quality kerosene, diesel and jet fuels. The light products from hydrocracking may also be rich in isobutane, an important raw material for alkylation.
In recent times, as the worldwide supply of light, sweet crude oil for refinery feedstock has diminished, there has been a significant trend toward conversion of higher boiling compounds to lower boiling ones. Due to this trend to heavier crude oil and the need for processing synthetic crude oil, hydrocracking has grown increasingly important. As demand for distillate fuels increases, refiners may incorporate hydrocrackers to convert, for example, vacuum gas oil (VGO) to jet and diesel fuel. Catalysts have been developed that exhibit desirable distillate selectivity, high conversion activity and stability for heavier feedstocks.
Accordingly, there is a need in industry for improving production of desirable hydrocarbons via hydrocracking of hydrocarbonaceous feedstock.